Skitch is a free app that helps you communicate visually with friends, co-workers, and the world. Annotate images with arrows, shapes, text, and more. Use Skitch to sketch something new, mark up maps, screen captures, or even a photo. Then save or share your Skitch annotation to help others see and understand your ideas.

Skitch is a great add on app for Evernote. You can sync Skitch items ugh your Evernote account across all you devices. I have created Skitch notes for job sites via a map, sent ideas about a website through a Safari screen shot, and diagramed a simple problem freehand.